<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .border {
      margin: 0 auto;

      width: 0;
      height: 0;
      border-bottom: 80px solid #9F9;
      border-top: 80px solid transparent;
      border-left: 80px solid transparent;
      border-right: 80px solid transparent;
    }

    .border::after {
      content: '';
      border-style: solid;
      border-width: 0 40px 40px;
      border-color: transparent transparent #96ceb4;
      position: relative;
      top: 0;
      left: 0;
    }
  </style>
</head>

<body>
  <div class="border"></div>
</body>

</html>